1. Field of the Invention
The present invention is related to a polymer electrolyte fuel cell and a polymer electrolyte fuel cell system.
2. Description of the Related Art
A polymer electrolyte fuel cell is made up of a unit cell composed of an anode layer, a cathode layer, a solid-polymer film disposed therebetween, a member having channels facing the anode layer, and a member which has channels facing the cathode layer.
The polymer electrolyte fuel cell is supplied with fuel gas, for example hydrogen-rich fuel gas, through the anode-side channels, and with oxidizer gas, such as air, through the cathode-side channels, thereby generating electricity through an electro-chemical reaction.
Most polymer electrolyte fuel cells in current use are composed of a plurality of separators and a plurality of unit cells that are stacked alternately in order to obtain a higher voltage. Here, each of the separators has fuel gas channels and oxidizer gas channels.
A problem faced by such polymer electrolyte fuel cells is that the heat generated during operation must be partially removed. Since heat radiation is not enough to maintain a predetermined temperature between about 50.degree. C. and 100.degree. C., most polymer electrolyte fuel cells have to be provided with cooling channels for each group of several unit cells.
As another problem, while a polymer electrolyte fuel cell is in operation, its solid-polymer film must be kept moist to maintain its ion conductivity. The water to be generated from the reaction between the fuel gas and the oxidizer gas contributes to the moistening of the solid-polymer film to some extent. However, since it is not sufficient, additional water must be supplied from outside the cell main body.
In view of these problems, most polymer electrolyte fuel cells are provided with a humidifier outside the cell main body to humidify the fuel gas and the oxidant gas, and further provided with cooling channels within the cell main body.
In contrast, Japanese Patent Publication No. 1-140562 (U.S. Ser. No. 076,970) discloses a polymer electrolyte fuel cell which moistens the solid-polymer film by supplying the fuel gas with water spray using an aspirator, and cools the cell main body by having the supplied water evaporate from the cathode layers.
However, the cooling performance of the water evaporation from the cathode layers is not sufficient for polymer electrolyte fuel cells that are large-sized or have a high output density.